Uranium recovery process



United URANIUM RECOVERY PROCESS No Drawing. Application January 4, 1955 Serial No. 479,873

6 Claims. (Cl. 23--14.5)

This invention deals with an improved method of processing uranium-containing materials such as uranium ores, and in particular with the recovery of the uranium from such materials by solvent extraction.

In extraction procedures of ores, the ore is customarily dissolved in an acid and the solution obtained thereby separated from any residue of insolubles, such as the gangue cake. The solution is then contacted with an organic, substantially water-immiscible solvent which selectively extracts some of the metal values present, usually those to be recovered. In order to remove from the solvent extract thus formed minor quantities of the less extractable values that have also been taken up by the solvent, a scrubbing procedure with an aqueous medium is usually applied to the solvent extract. After this the extracted values are removed from the solvent extract by back-extraction with water or an aqueous medium and the solvent is thereby regenerated for reuse.

In the case of uranium ores the raw material is usually digested With a strongly ionizing acid, preferably with nitric acid, and the insolubles are removed by filtration prior to subjecting the solution to solvent extraction. It has been found that a considerable part of the uranium is held by the residue, possibly by adsorption, and that therefore the uranium loss is considerable. For this reason a separate processing cycle was found necessary in order to recover the uranium held by the insolubles.

It is an object of this invention to provide a process for the recovery of uranium values from uranium-containing materials by solvent extraction by which the disadvantages discussed above are overcome.

It is another object of this invention to provide a process for the recovery of uranium values from uraniumcontaining materials by solvent extraction in which the uranium loss is very nominal and a high efficiency is thus accomplished.

It is still another object of this invention to provide a process for the recovery of uranium values from uraniumcontaining materials by solvent extraction in which filtration is eliminated.

It is also an object of this invention to provide a process for the recovery of uranium values from uraniumcontaining materials by solvent extraction which requires less operation, in particular no filtration and no second extraction cycle, and thus is more economical; the equipment for the process of this invention also requires less floor space than previous processes.

It is finally also an object of this invention to provide a process 'for the recovery of uranium values from uranium-containing materials by solvent extraction in which the separate processing of acid-insoluble residues is not necessary. I

These and other objects are accomplished by adding a strongly ionizing acid to the uranium-containing material, digesting the mixture obtained thereby whereby a digest slurry is produced, contacting said slurry with an organic, substantially water-immiscible solvent whereby the ura- Pat ffi ICC nium values in the solid as well as those in the liquid part of the slurry are taken up by said solvent and an extract phase is thus formed, and separating said extract phase from a slurry rafiinate.

The process of this invention is applicable to a great variety of uranium-containing materials, in particular to uranium ores such as pitchblende, and to concentrates obtained during the processing of uranium-containing ores or other raw materials such as black oxide, which principally is U 0 Another product for which the process has been found advantageous is the so-called -MgX which is a chemical precipitate that has been prepared in the Congo by adding magnesium hydroxide to a sulfuric acid leach solution of low-grade pitchblende ore; this slurry is digested with nitric acid of about 45% concentration at a temperature between 38 and 66 C. prior to extraction. A mixture of the raw materials just listed and of many others may also be used for the recovery process of this invention.

In Table I below, the compositions of pitchblende and MgX as typical representatives are given.

TABLE I Percent by Weight Component Pitchblende MgX The solid contents of the feed slurry may vary widely for the solvent extraction; however, in order to obtain optimal results the content should not be higher than 2 lbs./gal.; it also should not contain more than about 270 grams uranium per liter. Within these limits, feeds with a higher specific gravity have been found to yield a better uranium extraction than those of lower densities.

Organic solvents capable of extracting uranium from aqueous solutions are suitable for the process of this invention. Ethers, such as diethyl ether, nitromethane, ethyl benzoate and alkyl phosphates have given the most satisfactory results. The preferred solvent is tributyl phosphate, in particular when used in solution in an organic diluent. The concentration of the tributyl phosphate in the diluent, of course, has to be adjusted in accordance with the density of the slurry, because the solvent has to have a considerably lower specific gravity to obtain satisfactory phase separation. Kerosene is a very satisfactory diluent; a concentration of from 15 to 30% by volume of tributyl phosphate in kerosene has given the best results. Although diethyl ether performs highly satisfactorily, too, a considerably better uranium extraction and, at the same time, a lesser molybdenum and vanadium extraction occur with the tributyl phosphatekerosene mixture.

The acidity of the feed may vary widely; but a low acidity results in a more efiicient separation because less molybdenum, vanadium, silicon, phosphorus, etc. are then extracted. a

The solvent may be used without any acid or it may contain acid up to about 5 N. The addition of acidis' favorable in order to keep the acid centent' of the feed slurry'at a' constant value; However, it was found that in the case" ofdi'ethyl' ether" as" the" extractant' the" lower the acidity content is the lesswanadium and molybdenum valuesare. extracted. In .fact, for. ether the excess acidity the case of ether as solvent, while an acid, for instance nitric acidof a concentration-of 8N-,- wasfoundmost' advantageous for tributyl phosphate extr-actant. A volume ratio of 13:1 for organiczaqueous medium has given the content, i. e: th'atfree'acid'not formed by hydrolysis, is best results. In countercurrent operation it was found preferably: from 0to l N and in." this case extraction advantageous to carry out scrubbing at different temperais advantage'ously'carriedout with feed solutions in the" tures; the part of the column where the fresh water or range of no excess acid to a pH value of l. Underthese fresh acid isintroduced is preferably held at room temconditions optimaluranium extraction is achieved. The perature, while at the portion of the column where the situation is slightly different, though, for tributyl phosnonscrubbed extract contacts used scrubbing agent a temph'ate'as the" solvent where a higher acid concentration perature of about 50 C. is'preferably maintained. Unyieldsb'etter uraniumextraction and lesser molybdenum der these conditions the extraction of molybdenum, vaa'ndvanadium'extr-action. The optimal acid content for nadium, cadmium and the like was kept at a minimum. the feed inthe case of tributyl phosphateas the solvent The extract solution obtainedcan then be processed was-found" tobe about 3.6 N. 15 by various customary methods for uranium recovery.

It-Was aIsQfound'that, if the uranium extraction was The preferred procedure is back-extraction with an aquecarried out with neutral ether, the extraction was still ous medium, preferably water. The back-extraction is furthermoreimproved by adding, iron ions to the slurry. improved if the temperature of the water is raised to The iron ions can be added in the form of various about 50 to 100 C. The aqueous solution obtained compounds; for instance, the addition of siderite (FeCO thereby can then be treated by various methods; for in-' or aniline sludge (mainly Fe O has bene found atisstance, the aqueous solution can be evaporated to obtainfactory. uranyl nitrate hexahydrate or other uranium salt, depend Any equipment customary for extraction processes ing upon the type of acid originally used, and the salt can be used for carrying out the process of this invenis then decomposed by heating to uranium oxide. tion. The process can be conducted either as a batch In the following, an example is given for the purpose process or in a continuous manner, in the latter case of illustrating the high efliciency obtained with the countercurrent operation is preferred. For continuous process of this invention. The data given in this example countercu'rrent' extraction, extraction columns give the a e not to limit the scope of the invention. best results. These columns may be equipped with jet mixers, such as they are described and claimed in co- 39 Example pending'application Serial No. 359,646, filed by James A pitchblende-MgX process slurry was extracted H. Yeager et' al. on June 4, 1953. Another type of with a mixture of tributyl phosphate-naphtha in a concolumn which'has given excellent results is the so-called tinuous operation in a Scheibel column. Three runs pulse column, which is described and claimed in copendwere made each with a tributyl phosphate-70% ing:application Serial No. 325,003, filed on December naphtha mixture. The aqueous feed slurry contained" 9, 1952, by Leland L. Burger. Also the Scheibel column, about 225 grams of uranium per liter. The extractions patented by U; S. Patent No. 2,493,265 to Edward G. were carried out at a temperature of approximately 25 Scheibel on January 3, 1950, has been used successfully. C., and agitation was applied with a speed of' 2500 The flow rate of the feed slurry through the columns R. P. M. The scrub was always introduced at the top may vary between 1 liter/hr. and 60 gals/hr. depending 40 of the column, while the feed was introduced at aboutupon the size: and type of the column. The optimum the center of the column. The organic phase was the ratio of solvent:feed slurry was found to range between continuous phase. In Table II the operating conditions 1.8:! and 3:1. Agitation is advantageous to obtain a andextraction results are given, while in Table III-the' more intense contact between the three media, and a contents of contaminants in the uranium are listed.

TABLE I1 HNO3 Normality Uranium Raflinate Run N 0. Ratio, Feed: Feed, U Conc.,

Scrub: Organic ml./hr. g./l. Ext., Metal Feed Organic Scrub RatIJ Percent Percent 1. 0:0. 25:2. 3 757 4.1 0.0 0. 5 3. 4 0. 09 99. 92 1. mo. 26:2. 4 625 1. 3 0.0 3 0. 0 1. 0 0. 49 99. s 100 1.0=0.21=2.4 840 1.3 0.34 0.0 1.4 4.9 97.9 84

1 Excess HNO3 expressed as normality. 1 Based on rafiinate and feed analyses. 3 Water scrub.

TABLE III Spectrographic Analyses, Uranium Basis, p. p. 111. Run N0.

M0 v P Cr 00 Ni Pb B Fe s1 Cd Cu 20-10o 20 4N.D. N. D. N. D. 50 40 1 20 10-50 N. D 10 95 20 50 40 20 20 10 1 20 25 05 10 50 20 50 40 20 20 10 1 20 25 05 10 4 Not detected.

stirrer speed of between 2500 and 3000 R. P. M. has given-the best results. While either the aqueous slurry or the organic solvent may be the continuous phase, the latter is preferred.

Scrubbingycan -be carried out in the upper part of the extraction column, or else it may be done in a separate columni, Demineralized water has been found best for Good uranium recovery and decontamination were obtained in each run.

It will be understood that the invention is not to be limited bythe details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A process for recovering;uranium values from ura-v r J mum-containing solid materials comprising adding a strongly ionizing acid to said materials, digesting said materials with said acid whereby a digest slurry is ob- 6 phate is added in a mixture with a diluent and the tributyl phosphate content in said mixture is from 15 to 30% by volume.

5. The process of claim 2 wherein the solvent is ether and the acidity of the feed ranges from zero excess acid to an acidity yielding a pH of 1 and the acidity of the ether ranges from zero to a concentration of 1 N.

6. The process of claim 2 wherein the slurry contains about 2 lbs. of solids per gallon.

References Cited in the file of this patent UNITED STATES PATENTS 2,227,833 Hixson et al. Jan. 7. 1941 

1. A PROCESS FOR RECOVERING URANIUM VALUES FROM URANIUM-CONTAINING SOLID MTERIALS COMPRISING ADDING A STRONGLY IONIZING ACID TO SAID MATERIALS, DIGESTING SAID MATERIALS WITH SAID ACID WHEREBY A DIGEST SLURRY IS OBTAINED, CONTACTING SAID DIGEST SLURRY WITH AN ORGANIC SUBSTANTIALLY WATER-IMMISCIBLE SOLVENT WHEREBY THE URANIUM ARE TAKEN UP BY SAID SOLVENT AND AN EXTRACT PHASE IS FORMED, AND SEPARATING SAID EXTRACT PHASE FROM A SLURRY RAFFINATE. 